1. Field of the Invention
The present invention relates to a piezoelectric driving body and an ultrasonic motor having a piezoelectric element as a driving source, and to an electronic apparatus such as an electronic timepiece, a medical equipment, an optical information apparatus, a camera and the like.
2. Description of the Related Art
Various ultrasonic motors have been proposed which employ circular or annular vibrating bodies oscillated in a circumferential direction of the vibrating body to thereby drive a moving body. Such an example is shown in Japanese Patent Publication No. 7750/1994.
Meanwhile, it is known as a manufacturing method of a vibrating body to manufacture through cutting generally from a vibrating body shape by an automatic lathe or the like.
On the other hand, recently there is a proposal on an ultrasonic motor utilizing a micro-machining technology such as etching. Such an example is disclosed, for example, in Japanese Patent Laid-open No. 337052/1998.
However, because the conventional ultrasonic motors as disclosed in Japanese Patent Publication No. 7750/1994 utilize deflection-vibration in a circumferential direction of the vibrating body, the vibrating body must have been increased in plate thickness in order to obtain displacement in a feed direction of the moving body, i.e. displacement in a circumferential direction, thus incurring increase in resonant frequency. Particularly, the resonant frequency has been increased with increase in the number of waves in the circumferential direction and the number of nodes with respect to a radial direction. Furthermore, because of having protrusions for magnifying displacement, the thickness of the ultrasonic motor has been increased. Also, the increase of manufacture cost has been incurred due to forming one by one vibrating bodies by machining.
Meanwhile, in the structure shown in Japanese Patent Laid-open No. 337052/1998, a large output cannot be obtained because the piezoelectric element is small in area. Further, because the structure has a plurality of cantilevers, the resonant frequency deviates between the cantilevers thus having a problem with deviation in individual motor characteristics. Furthermore, there is the disadvantage that the direction of rotation is in only one direction.
In view of the above problems, the present invention realizes an ultrasonic motor capable of suppressing an increase in resonant frequency and obtaining a great amplitude even if made smaller, and it is an object to provide an excellent-quality ultrasonic motor that is simple to manufacture and mass produce, and to provide an electronic apparatus having the ultrasonic motor.
In order to achieve the above object, an ultrasonic motor of the present invention is characterized, in an ultrasonic motor having a vibrating body in a quadrilateral plate form, a piezoelectric element bonded on the vibrating body, a protrusion provided on the vibrating body, and a moving body in contact with the protrusion to be driven by same, in that the piezoelectric element oscillates a vibration wave having a node on a diagonal line of the vibrating body or on lines with which the vibrating body is divided into two and four, and the protrusion being provided in a position off the node. With this structure and principle, it is possible to obtain a vibration component required for driving the moving body regardless of the plate thickness of the vibrating body and reducing the thickness of the vibrating body and further the ultrasonic motor overall. Also, because the resonant frequency of the vibrating body can be decreased, a great amplitude can be obtained even if made smaller thus realizing an efficient ultrasonic motor.
By providing a plurality of electrodes on the piezoelectric element disposed on the vibrating body and either selecting an electrode to which a drive signal is applied or changing the phase of a drive signal, the node of vibration to be oscillated by the vibrating body can be moved to vary a direction of rotation of the moving body.
According to this invention, because the vibrating body is quadrilateral in shape, a multiplicity of vibrating bodies can be formed at one time by dicing or the like. Even if blanking is made using a press or the like, material can be effectively utilized without leaving the remainder.
Also, in the piezoelectric driving body for including an ultrasonic motor of the invention, the polarizing directions of the piezoelectric element having a plurality of electrode portions are all made in the same direction. Due to this, for example, it is possible to suppress or make even deformation caused where polarization is made after the piezoelectric element is bonded to the vibrating body. The contact situation with the moving body contacting the vibrating body becomes favorable. By polarizing the entire piezoelectric element in the same direction at one time, polarization is favorably provided without impeding required deformation of the piezoelectric element during polarization, and thus making it possible to obtain a large drive force from the piezoelectric vibrating body.
Also, by providing an ultrasonic motor or piezoelectric driving body of the invention on an electronic apparatus, it is possible to realize the reduction of size, thickness and consumption power for the electronic apparatus.